1. Field of the Invention
This invention relates to a dynamic RAM used in semiconductor memory systems.
2. Background of the Invention
In recent years, the width of circuits in semiconductor devices has decreased. This reduction in circuit width has increased the capacity of semiconductor memory. As memory capacity increases, the memory is referred to as large scaled. As memory size increases, memory efficiency is a desired quality. Logic-hybrid memory includes a logic block that functions beyond merely controlling reading and writing to specific memory cells. Logic blocks also control a signal called an I/F signal that performs an interface (I/F) between the logic block and the memory block.
An example of this type of semiconductor where the semiconductor chip includes a logic circuit and a memory is described in "A 500-Megabyte/n Data-Rate 4.5M DRAM" Kushiyama et al., IEEE Journal of Solid-State Circuits Vol. 28, No. 4, April 1993. This article illustrates in FIGS. 4 and 10 and describes a memory block (DRAM CORE) and a logic block (INTERFACE LOGIC) in a chip. Signals, such as /RAS, /CAS, and an address signal are control signals from the exterior of the chip, or in a conventional memory chip are the interface (I/F) signals sent between the logic block and the memory block. The I/F signals are basic signals for control of the logic block and operations of the memory block.
Usually, the logic block controls the I/F signal so that the memory block can operate normally. However, problems occur when the logic block does not operate normally. This may be due to abnormal signals generated by the logic block operating in an unstable state. Often these unstable states occur immediately after power is turned on. Other events causing abnormal signals are temporary, unexpected wave forms from the logic block due to various external factors, such as a changing power source or a change in temperature during a burn-in examination.
When memory block receives the an abnormal signal, dangerous, large currents can be generated damaging the internal circuit of the memory block. This event may cause latch up and can fatally damage the semiconductor package or circuit board. If the memory block is not initialized correctly, the reading and writing operations normally performed when the power source is turned on cannot be performed. The problem of conventional logic-hybrid memory is the logic block and the memory block are connected to each other only through the I/F signal. No mechanism protects the memory block against abnormal signals generated by the logic block.